Launched in 1977, Voyager 1 has survived far beyond anything its designers could reasonably have expected. Nearly five decades later, the spacecraft remains in communication with Earth as it travels through interstellar space, making it the longest-operating and most distant human-made object ever sent from Earth.
Voyager 1 transformed our understanding of Jupiter and Saturn before beginning an entirely different mission beyond the planets. Its extraordinary longevity has since allowed scientists to make direct measurements of conditions beyond the Sun’s heliosphere. Here are ten remarkable facts about one of the most successful spacecraft ever built.
1. Voyager 1 Is the Most Distant Human-Made Object
Voyager 1 launched on September 5, 1977, just 16 days after Voyager 2. Despite launching second, Voyager 1 followed a faster trajectory and overtook its twin before reaching Jupiter.
It is now the most distant human-made object from Earth and continues to increase that distance as it travels outward at roughly 17 kilometers (10.5 miles) per second relative to the Sun.
The spacecraft is so distant that radio signals traveling at the speed of light take many hours to make the one-way journey between Earth and Voyager 1. NASA communicates with it through the Deep Space Network’s giant radio antennas.
2. Out of an Earlier Grand Tour Concept
The origins of Voyager stretch back to plans developed during the 1960s for a rare alignment of the outer planets. Engineers realized that a spacecraft could use the gravity of one planet to redirect and accelerate it toward the next, allowing several worlds to be explored during a single mission.
Early concepts were associated with NASA’s Mariner spacecraft program, and the probes that eventually became Voyager were initially known as Mariner Jupiter-Saturn 1977. As the spacecraft design became increasingly sophisticated, NASA established Voyager as a separate mission.
Voyager 1 ultimately flew past Jupiter in March 1979 and Saturn in November 1980. Its close encounter with Saturn’s moon Titan sent it onto a trajectory away from the plane of the planets, ending the possibility of further planetary encounters but beginning its journey toward interstellar space.
3. Voyager 1 Is Powered by Radioactive Decay
Voyager 1 does not use nuclear reactors. Instead, it carries three radioisotope thermoelectric generators (RTGs), which convert heat produced by the radioactive decay of plutonium-238 into electricity.
The RTGs produced about 470 watts of electrical power when Voyager launched. Their output has steadily declined as the plutonium decays and the thermocouples age, forcing mission engineers to manage an increasingly limited supply of electricity.
NASA has progressively switched off heaters and scientific instruments to extend the mission. Remarkably, Voyager 1 was still operating in 2026, almost half a century after launch.
4. Voyager 1 Is on an Escape Trajectory from the Sun
After its encounters with Jupiter and Saturn, Voyager 1 had sufficient velocity to continue outward indefinitely rather than returning toward the planets. It joined Pioneer 10 and Pioneer 11 as one of the first spacecraft placed on trajectories that will eventually carry them far beyond the Sun.
Voyager 1 travels outward at about 17 km/s relative to the Sun. Voyager 2 and New Horizons are also following escape trajectories, although Voyager 1 remains much farther away than either of them.
This does not mean the spacecraft has already escaped every part of the solar system. The enormous Oort Cloud, whose icy objects remain gravitationally bound to the Sun, extends vastly farther than Voyager has yet traveled.
5. Helped Reveal Saturn’s Unusual Atmosphere
During its November 1980 Saturn encounter, Voyager 1 returned detailed measurements of the planet’s atmosphere, rings, magnetic environment and moons.
One important puzzle concerned Saturn’s helium abundance and its unexpectedly large internal heat output. Scientists have proposed that helium can separate from hydrogen deep inside the planet and fall toward its interior. This process releases gravitational energy as heat and may contribute to Saturn radiating substantially more energy than it receives from the Sun.
Voyager also measured extraordinarily fast winds in Saturn’s atmosphere, with speeds around the equator reaching hundreds of meters per second.
6. Discovered Active Volcanoes on Io
One of Voyager 1’s greatest discoveries came during its 1979 encounter with Jupiter. Images of Io revealed enormous volcanic plumes rising above the moon’s surface.
It was the first time active volcanism had been observed on another world. Io is continuously flexed by the competing gravitational pulls of Jupiter and its neighboring moons, generating immense amounts of heat inside the moon and making it the most volcanically active body known in the solar system.
Voyager’s instruments also detected material associated with Io throughout Jupiter’s magnetic environment, revealing how strongly the small moon influences the entire Jovian system.
7. Took the Solar System’s First Family Portrait
On February 14, 1990, Voyager 1 turned its cameras back toward the planets and took a sequence of 60 images from roughly 3.7 billion miles (6 billion kilometers) away.
The resulting Family Portrait of the Solar System included six planets: Venus, Earth, Jupiter, Saturn, Uranus and Neptune. Mercury was too close to the Sun to photograph safely, Mars was lost in scattered sunlight, and Pluto was too small and faint to appear.
After completing the sequence, Voyager 1’s cameras were permanently switched off. The spacecraft had no more planetary encounters ahead, and shutting down the imaging system helped conserve resources for its long interstellar mission.
One frame became particularly famous. Earth appears as a tiny point of light suspended in a ray of scattered sunlight. The photograph became known as the Pale Blue Dot and inspired Carl Sagan’s famous reflection on Earth’s place in the cosmos.
8. Voyager 1 Entered Interstellar Space in 2012
On August 25, 2012, Voyager 1 crossed the heliopause, the boundary where the solar wind and magnetic influence carried outward by that wind give way to the interstellar environment.
Measurements showed a dramatic decrease in particles originating from inside the heliosphere and an increase in energetic particles arriving from interstellar space. Plasma measurements later helped confirm that Voyager had crossed into the interstellar medium.
Voyager 1 thereby became the first human-made spacecraft to enter interstellar space. Voyager 2 followed in November 2018.
9. Has Not Yet Left the Solar System
Entering interstellar space does not necessarily mean Voyager 1 has passed beyond everything gravitationally associated with the Sun.
The heliopause marks the outer boundary of the heliosphere, the enormous bubble produced by the solar wind. The Sun’s gravitational domain extends much farther and includes the distant Oort Cloud, a vast reservoir of icy bodies thought to surround the planetary system.
At its present speed, Voyager 1 will take roughly 300 years to reach the inner region of the Oort Cloud and perhaps around 30,000 years to travel beyond its distant outer edge.
In about 40,000 years, Voyager 1 will pass within roughly 1.6 light-years of the star Gliese 445. By then, however, the spacecraft will have been silent for tens of thousands of years.
10. Voyager 1 Carries Earth’s Golden Record
Voyager 1 and Voyager 2 each carry a gold-plated copper record intended as a message from Earth should either spacecraft ever be discovered by another civilization.
The Voyager Golden Record contains sounds of Earth, music from different cultures, spoken greetings in dozens of languages and images describing life and our planet. Instructions engraved on its cover explain how the record can be played and identify the location of the Sun using pulsars as cosmic landmarks.
Among its more unusual contents is a recording associated with writer and Voyager project contributor Ann Druyan. Her brain waves and other physiological signals were recorded while she thought about subjects including human history and the experience of falling in love.
The chances of anyone ever finding the record are extraordinarily small. Yet long after Voyager 1 can no longer communicate with Earth, the spacecraft and its Golden Record will continue traveling through the Milky Way as artifacts of the civilization that sent them.